The invention relates to a vehicle brake disc with a wear indicator.
As a result of high demands on safety-relevant components in vehicles, a brake disc thickness in a vehicle is measured at regular intervals so that the brake disc can be replaced in good time. An inadequate brake disc thickness increases the risk of heat cracks and the risk of severe wear of the brake linings up to failure of the brake disc. In order to avoid premature replacement of the brake disc and unnecessary time in the garage, it is furthermore necessary to be able to ascertain the remaining service life which is still available. In the case of commercial vehicles, this measuring process normally requires a pit or removal of the wheels which is time-consuming. It can also be very difficult for a lay person to carry this out himself or herself.
It is known from practice to normally use micrometer screws in order to measure the state of wear of the brake disc or the thickness of the brake disc. This is necessary since a ridge is often retained on the outer edge of the brake disc, which ridge does not allow the use of a gauge or a conventional sliding calliper.
It is furthermore known from the prior art to provide wear features, also referred to below as wear indicators, in the brake disc friction surface in the form of a recess, pocket, groove, bore or chamfer. In this case, different embodiment variants are known which may differ according to three aspects:
According to a first aspect, variants are known in which the wear features appear with increasing wear and can be seen to their full extent in the case of terminal wear, e.g., EP 1 108 918 B1. Variants are furthermore known in which the wear features disappear with increasing wear and can no longer be seen in the case of terminal wear, e.g., DE 10 2005 032 638 A1.
According to a second aspect, wear features are known which only mark the terminal state of wear, e.g., U.S. Pat. No. 6,457,566 B1, and wear features which enable a continuous reading off of the state of wear, e.g., US 2013/0299284 A1. The brake disc known from laid-open application US 2013/0299284 A1 has depressions with different diameters which are incorporated in the rear side of the friction ring. With increasing wear, these are covered and can then only be interpreted in terms of brake disc wear with the aid of a measuring gauge.
According to a third aspect, variants are known in which wear features are distributed over the circumference in order to ensure a better view or in the case of which several features are additionally provided which are distributed radially on the brake disc in order to be able to ascertain a radial or concave oblique wear, e.g., EP 1 108 918 B1.
The described wear features usually, however, only represent a “black and white” display, i.e., in the event of a complete disappearance of the wear gauge, it can assumed that a defined threshold value has been reached at the corresponding point of the brake disc. Interim states and the continuous progression of wear can, however, as described in US 2013/0299284 A1, only be ascertained with an additional measurement tool as a reference which furthermore requires direct access to the brake disc.